This invention relates generally to the art and technology of thermal ink jet printing and more particularly to a new and improved thin film resistor (TFR) printhead architecture and geometry which is used in the manufacture of disposable thermal ink jet (TIJ) pens.
In the design of the thin film resistor printheads used in the manufacture of thermal ink jet pens, it has been a common practice to photolithographically define and electrically interconnect a plurality of heater resistors, such as those made of tantalum aluminum, on a thin film substrate and then construct a corresponding plurality of aligned firing chambers and associated orifice openings above and adjacent to the heater resistors. These firing chambers and orifice openings are used in ejecting ink from a region within the firing chambers and above the heater resistors and onto a print medium. As is well known, these firing chambers have commonly been constructed of a selected polymer material disposed on the TFR substrate and on top of which an orifice plate such as a gold plated nickel material is disposed and aligned with respect to the firing chambers. The polymer barrier layer is also photolithographically defined so as to have a predetermined firing chamber geometry and pattern adjacent to which an ink feed channel or port is used to fluidically connect each firing chamber with a source of ink supply.
In operation, electrical drive pulses are selectively applied to conductive traces leading into the various heater resistors situated in the bottom of each firing chamber to thereby heat the ink to boiling in each firing chamber and above each heater resistor. This resistor firing in turn produces a vapor bubble and a corresponding pressure field within the firing chamber used for thermally ejecting ink onto an adjacent print medium.
In one general architecture of firing chambers, the cross-sectional geometry of the firing chambers defined by the walls of the polymer barrier located between the thin film resistor substrate and the orifice plate was partially rectangular in shape and of a three sided wall construction. The firing chambers and ink flow ports connected thereto function not only to define an ink flow path and ink firing chamber for each heater resistor, but this architecture also serves to fluidically isolate adjacent heater resistors and thereby minimize undesirable crosstalk therebetween.
Examples of the above three sided rectangular shaped barrier layer geometries are those used in the three color disposable pen adapted for use in Hewlett Packard's PaintJet thermal ink jet printer. This disposable pen and the PaintJet thermal ink jet printer in which it has been successfully used are described in further detail in the Hewlett Packard Journal, Volume 39, No. 4 August 1988, incorporated herein by reference. The general architecture of the orifice plate and ink feed geometry for the above PaintJet pen is also described in U.S. Pat. No. 4,771,295, issued to Jeffrey P. Baker et al., assigned to the present assignee and also incorporated hereby by reference.
The three-sided firing chambers are commonly utilized with rectangularly shaped heating resistors which are typically positioned with their edges within the enclosed region defined by the downward extension of the chamber walls.
Whereas the above Hewlett Packard thermal ink jet pen designs of three-sided barrier layer and firing chamber construction have performed quite satisfactorily under most conditions of operation, there are nevertheless certain situations where the above three-sided rectangular-shaped barrier layer designs have not been totally suitable for producing acceptably uniform ink drop volumes, printed dot and line uniformity and a corresponding acceptable print quality, particularly during sustained high frequency operation of the thermal ink jet pen. It is the solution to this problem to which the present invention is directed.